This proposal seeks funding for a versatile X-band/Q-band electron paramagnetic resonance (EPR) spectrometer. The group of major users consists of Professors Judith Klinman, James McCusker, Kenneth Raymond, Kenneth Sauer, David Wemmer, and Drs. Melvin Klein and Vittal Yachandra of the Physical Biosciences Division of the Lawrence Berkeley National Laboratory. The research interests of this group of scientists span metalloenzyme chemistry, bioinorganic chemistry, electron transfer, neurobiochemistry, and photosynthesis. This proposal describes how, in each of these areas, EPR spectroscopy can play a vital role in the identification and characterization of chemical and biochemical systems, as well as helping to elucidate mechanisms of protein function and electron transfer pathways in photo-induced electron transfer processes. For example, Professor Klinman's research is concerned with the mechanism of activity in a wide range of Cu- and Fe-containing enzymes. EPR spectroscopy can be utilized both to characterize the metal-based active site(s) of the enzyme as well as identify intermediates in the overall biochemical process being studied. Professor Sauer and Drs. Klein and Yachandra work on the oxygen-evolving complex of photosystem II, using EPR spectroscopy extensively to help characterize species involved in the conversion of H20 to O2. Professor McCusker's research concerns the correlation between electron exchange and electron transfer in polynuclear clusters such as those found in electron transfer proteins. EPR can be used to identify electron transfer photoproducts as well as help to characterize the electronic structures of the clusters themselves. Professor Raymond's research is also in the area of bioinorganic chemistry, where EPR spectroscopy is an important technique for the characterization of Fe siderophores, as well as interatomic interactions in supramolecular assemblies. Finally, Professor Wemmer's research on the structural dynamics of the prion protein can utilize EPR spectroscopy to determine the structure of the protein by taking advantage of the long distance over which unpaired spins can interact, complimenting the local and short-range structural information afforded by his NMR techniques. All of these groups have a clear need for routine access to an EPR spectrometer, yet the University of California at Berkeley does not have such an instrument. This proposal therefore seeks funding for the acquisition of a state-of-the-art spectrometer with variable-temperature (1.8 - 400 K) as well as both X-band (ca. 9 GHz) and Q-band (35 GHz) capabilities. We believe that this investment on the part of the Institute will greatly enhance not only the research of the major user group, but of the Department of Chemistry at UC Berkeley as a whole.